The key on-off trick started in 99 and was on all trucks by 00. Take the key in the ignition and turn it in the following sequence : ON - OFF - ON - OFF - ON. Then watch the digital odometer for the codes. If the odo stays on the mileage then your truck won't do it. If it works though you will see P ECU, then the codes if any, if none you will see --------, then P PCM, any codes then P DONE.

Not all codes can be read this way and you can't clear them this way either. Not all code readers can get the codes out or cleared either. There is definetly one scan tool that will get them out and that is a proprietary scan tool called the DRB III that all DC dealer mechanics use. They are very expensive if you want to buy one.